Star Trek: 10 Things You Didn't Know About Combadges
1. The Earliest Starfleet Combadge We've Seen
As mentioned in the intro, combadges were first seen in The Next Generation. In The Original Series and the TOS films, the entire Federation (apart from agents of Section 31) used communicators instead, which were small, more phone-shaped devices. However, there's one scene that gives us a hint that they were introduced long before Picard's time.
In the Next Generation episode Yesterday's Enterprise, there's a scene where we see Lieutenant Richard Castillo, a time-travelling visitor from the Enterprise-C, tapping on his badge and talking into it. Lieutenant Castillo came from 22 years in the past, back when Starfleet still used the stylish red uniforms from the TOS films, which makes one wonder when exactly the change was made from ordinary badges to combadges.
The scene was probably just included because the team behind the episode simply forgot that the badges from the TOS films were never used as communicators, but the characters from the episode came from a point in time decades after the Enterprise-B launched in Star Trek: Generations, so combadges being invented within this period fits in the timeline well enough for us to consider it canon.